1. Field of the Invention
The present invention relates to an optical system for generating a light beam, together with an optical module comprising such an optical system.
2. Description of the Related Art
Although not exclusively, the optical system and the optical module according to the invention are designed to equip motor vehicles, the light beam generated then fulfilling a lighting function (for example low beam, high beam, fog beam) or a signalling function (for example position lights, direction indicator lights, brake indicator lights, reversing lights, rear fog lights, daytime lights).
An optical system is already known from the document FR 2 919 913 for generating, from a single light source and along an optical axis, a composite light beam composed of a plurality of light beams amongst which are a central light beam and a peripheral light beam surrounding the central light beam. This reference is incorporated herein by reference and made a part hereof. For this purpose, a collimator is disposed in the neighborhood of a single light source, for example, a light-emitting diode (LED) capable of emitting light in a Lambertian fashion into a half-space, this source being situated on the optical axis of the optical system.
This collimator is generally fabricated from a single monolithic piece, with symmetry of revolution about the optical axis, and whose external profiles have particular shapes capable of generating the central beam and the peripheral beam. More precisely, on a first side where the light source is disposed, the external profile of the collimator has a central portion and a peripheral portion mutually joined together via a cylindrical intermediate portion and, on a second side opposing the first side, a plane downstream portion perpendicular to the optical axis. The central portion has a convex shape, with a focal point situated at the source. The peripheral portion has a parabolic shape, whose focal point is also situated at the light source.
Thus, the central light beam is generated by refraction of the light rays emitted by the light source on the central portion of the external profile of the collimator, the light rays of the central light beam then being parallel to one another and also parallel to the optical axis. With regard to the peripheral light beam, this is generated by refraction of the light rays emitted by the light source on the intermediate portion, then by total internal reflection of these same light rays on the peripheral portion of the collimator, the light rays of the peripheral light beam being parallel to those of the central light beam and the peripheral light beam surrounding the central light beam.
The composite light beam thus generated, which comprises the central and peripheral light beams, is designed to be directed towards an optical diffuser equipped with a plurality of microstructures arranged to produce an illumination which, in a plane orthogonal to the optical axis of the collimator, exhibits certain features linked to the regulations in force for the road lights and/or signaling lights for motor vehicles that it is designed to form, notably relating to the uniformity and the angular opening of the beam. This optical diffuser can either take the form of a screen (equipped with microstructures) placed as close as possible to the collimator, or, preferably, take the form of microstructures fabricated directly as part of the collimator. In the case of a monobloc system, it will be noted that the microstructures can only be placed on the exit face of the diffuser.
The collimator described in the aforementioned document FR 2 919 913 is particularly advantageous in the respect that it is formed as a single monolithic piece, which can be fabricated in a simple manner using a mould with a complementary shape to that of this piece, and that it allows all of the light intensity emitted, into a half-space, by the light source to be effectively redirected.
However, the angular opening of the composite light beam generated by a collimator of the monobloc type is limited by the total internal reflection limiting angle of the microstructures that form the optical diffuser, within which the light rays coming from the collimator must be refracted. In particular, for a composite light beam with rays parallel to one another and parallel to the optical axis, this limiting angle leads to a maximum angular opening of around 35°. However, although the regulations applicable to the majority of the lights for motor vehicles require angular openings less (for example 20°) than this limiting angle, a wider angular opening is on the contrary required for certain of these lights. For a reversing light, for example, the horizontal angular opening must be of the order of 45° (with a light intensity at 45° close to 15 to 20% with respect to the total light intensity) and the vertical angular opening must be around 5°.
It is furthermore known, from the document EP 2 230 446, that in order to overcome this limitation, it is possible to use an additional screen as optical diffuser on which the microstructures are placed on the entry face of the diffuser element. This configuration allows a lighting and/or signaling beam to be obtained, after passing through the optical diffuser, having an angular opening wider than the opening limit resulting from the total internal reflection limiting angle for microlenses with a concave surface, the resulting horizontal angular opening of the light beam thus being able to reach for example angles equal to 45° or 50°.
However, this solution involves the addition of at least one intermediate optical element, which therefore makes the optical module more complex to manufacture. In this case, it is necessary to align these elements. Such an optical module is furthermore more costly and bulky, and, moreover, leads to additional losses of light due to the Fresnel coefficients (of around 15 to 20%).